1. Field of the Invention
This invention relates to a detergent composition which possesses excellent resistance to hard water, in which the amount of sodium tripolyphosphate employed as a builder can be greatly reduced or sodium tripolyphosphate can be entirely omitted, and which possesses an excellent rinsing property after washing.
2. Description of the Prior Art
Although the demand for sodium tripolyphosphate as a builder component in detergents has been increasing, various limitations have been imposed on the use of this builder because of the wide-spread shortage of phosphate rock, its high price and the like. Further, it is known that phosphate components contained in discharged washing solutions cause eutrophication and pollution in rivers and the lakes. Accordingly, in the detergent art, there have been serious problems of how to reduce the amount of sodium tripolyphosphate and how to utilize it more efficiently in detergents.
Various attempts have heretofore been made to solve these problems, and these known attempts are generally divided in two types; one type is directed to a method in which another builder is used as a substitute for sodium tripolyphosphate and the other type is directed to a method in which a surface active agent possessing excellent resistance to hard water is used as the effective detergent component. In the former method, however, there has not been discovered any practical builder that can be used instead of sodium tripolyphosphate and that will provide satisfactorily good results with respect to washing ability, cost and other factors, safety and the like. In the latter method, the use of hard water-resistant polyoxyethylene alkyl ether sulfates (hereinafter referred to simply as "ether sulfates" or "ES"), which are salts of sulfuric acid esters of adducts of 3 to 5 moles of ethylene oxide to higher alcohols having 12 to 18 carbon atoms in the alkyl group, has been proposed and practiced. These ether sulfates, which have been effectively used for detergents, have a good resistance to hard water, but they have a foaming characteristic such that foaming increases with an increase of water hardness at low concentrations. This characteristic makes it difficult to remove foam during the rinsing step after washing. In fact, in the case of ether sulfate-containing detergents for clothing, tableware, hair, furniture or the like, foams do not disappear smoothly and sufficiently during the rinsing or finishing step. This defect in rinseability decreases the commercial value of detergent products. Accordingly, if this defect can be ameliorated, it will be possible to provide a phosphate-free or low phosphate detergent having a high commercial value and which can be easily used by consumers with saving of rinsing water.
In order to overcome the foregoing defects, we previously proposed, in the U.S. Patent Application Ser. No. 663,912 filed on Mar. 4, 1976, a detergent composition including an ether sulfate of a special structure having a greatly reduced number of carbon atoms in the alkyl group, a high branching ratio and a greatly reduced number of moles of added ethylene oxide, which special ether sulfate had heretofore not been used in the detergent art, which detergent composition had a high resistance to hard water and a greatly improved rinsing property.
Since soils adhered on fabrics contain various oily components differing in the polarity, when surface active agents suitable in its affinity for respective oily components are used, these oily soils can be washed away more readily. Accordingly, in the above detergent free of sodium tripolyphosphate (phosphate-free) or having a reduced sodium tripolyphosphate content (low-phosphate) which has a high washing power, it is expected that if ether sulfates of other types are used in combination, the washing power will be further improved. In general, by adding of these other types of ether sulfate, excellent washing power due to high resistance to hard water may be obtained, but the rinsing property, another important property, is degraded.